1. Field of the Invention
The invention relates to an ion sensor for measuring ion concentration of a solution, more particularly to an ion sensor including a plurality of ion-sensitive nanorods protruding from a conductive base structure.
2. Description of the Related Art
Ion sensors are useful for measuring concentration of anion of interest in a solution, and can selectively absorb the ions on a surface thereof, which induces a surface potential thereat due to the total charge of the absorbed ions. Hence, by measuring the surface potential of the ion sensor, the ion concentration of the solution can be determined.
U.S. Pat. No. 4,180,771 discloses a chemical sensitive field effect transistor that includes a semiconductor substrate having a source region and a drain region, a gate dielectric film formed on a top side of the semiconductor substrate, three electrodes formed on the source region, the drain region and the gate dielectric film, respectively, a chemical sensitive film formed on a bottom side of the semiconductor substrate, and a reference electrode formed on the chemical sensitive film. In use, when the chemical sensitive film is brought into contact with a solution for measuring ion concentration of the solution, a surface potential of the chemical sensitive film is changed, which, changes the electric field in the semiconductor substrate, which, in turn, changes the conductivity of a channel region of the semiconductor substrate between the source region and the drain region. Hence, by measuring the current passing through the source region and the drain region of the semiconductor substrate, the ion concentration can be determined.
U.S. Pat. No. 4,446,474 discloses an ion sensitive field effect transistor (ISFET) that includes a semiconductor substrate having a source region and a drain region, a gate dielectric film formed on the semiconductor substrate, an inorganic insulator protecting film formed on the gate dielectric film, and a sensitive film formed on the inorganic insulator protecting film and capable of absorbing selectively ions to generate a surface potential for measuring ion concentration.
U.S. Patent Application Publication No. 2006/0220092 discloses an extended gate field effect transistor (EGFET) ion sensor that includes a semiconductor silicon substrate, a titanium dioxide sensitive film formed on the semiconductor silicon substrate, and a metal-oxide-semiconductor-field-effect transistor (MOSFET) connected electrically to the titanium dioxide sensitive film through a conductive wire. In use, only the assembly of the semiconductor silicon substrate and the titanium dioxide sensitive film is needed to be immersed in the solution for measuring ion concentration of the solution through a buildup surface potential at the surface of the titanium dioxide sensitive film.
U.S. Patent Application Publication No. 2007/0001253 discloses an extended gate field effect transistor (EGFET) ion sensor that includes an ion sensitive component and a MOSFET connected electrically to the ion sensitive component. The ion sensitive component includes a glass substrate, an indium tin oxide (ITO) film formed on the glass substrate, a tin oxide sensitive film formed on the ITO film, and an enzyme chemical film formed on the tin oxide sensitive film.
U.S. Pat. No. 6,464,940 discloses a pH sensor that includes a semiconductor substrate (n-type silicon substrate with an n-channel), a silicon dioxide sensitive film formed on a top side of the semiconductor substrate, a liquid storing part formed on the silicon dioxide sensitive film, a first electrode formed on the liquid storing part, and a second electrode formed on a bottom side of the semiconductor substrate. When a solution to be analyzed is fed into the liquid storing part to contact the silicon dioxide sensitive film, a surface potential at a contact surface of the silicon dioxide sensitive film is produced and the capacitance of the n-channel is changed. Hence, by measuring the capacitance and the voltage of the pH sensor, ion concentration of the solution can be determined.
U.S. Patent application Publication No. 2008/0277746 discloses a nanowire sensor with self-aligned electrode support. The nanowire sensor includes a doped silicon-containing substrate, a growth-promoting metal layer formed on the silicon-containing substrate, a silicon nitride support formed on the growth-promoting metal layer, a plurality of nanowires formed on the growth-promoting metal layer, and a top electrode formed on top ends of the nanowires. The top electrode also plays a role of protecting the nanowires from damage. It is noted that since the top electrode is formed on the top ends of the nanowires, the nanowire sensor can only be used for detecting gases. If the nanowire sensor is to be used for detecting ions in a solution, the potential of the top electrode tends to be interfered by the ions in the solution, which can cause the function of the nanowires to fail.
The whole disclosures of the aforesaid patents are incorporated herein by reference.